GTP binding proteins play diverse and important roles in cellular physiology, including: signal transduction; protein translation; vesicle transport; transport through nuclear pores; translation of secreted proteins; transport of proteins into chloroplasts; and organization of the cytoskeleton. G proteins can occur in GDP- and GTP-bound forms, each of which has distinct properties. Various cellular effectors promote GTP hydrolysis (conversion to the GDP-bound form) or release of GDP and acquisition of a new molecule of GTP (conversion to the GTP-bound form). The GTPase cycle operates as a binary switch to assure the fidelity of cellular processes. The switch is used to effect information transfer and to assure appropriate interactions between molecules or organelles, for example, delivery of the proper aminoacylated tRNA to the ribosome or the binding of a membrane vesicle to the proper target membrane. A new subfamily of G proteins was discovered recently, called developmentally regulated GTP binding proteins or DRGs (based on the naming of a mouse clone). DRG clones have been isolated from mammals, fission and budding yeasts, insects, amphibians, nematodes and archaebacteria. Amino acid sequence identity is very high; for example, human and fission yeast proteins are 65% identical. A DRG clone from pea was isolated in this lab and an Arabidopsis clone was obtained from the ABRC (called PsDRG1 and AtDRG1, respectively). Amino acid identity between the plant clones is 89% and identity between plant and human DRGs is 66%. PsDRG1 mRNA accumulates in growing stems and axillary buds (relative to their non-growing counterparts), but it also accumulates in organs that are not growing (leaves and carpels). Beyond this and related studies in other organisms, little is known about possible functions of DRGs. The high level of sequence conservation suggests that DRGs participate in some important and highly conserved cellular activity. The primary goal of this proposal is to deduce aspects of DRG function using transgenic Arabidopsis plant's. 1) Arabidopsis libraries will be screened for additional DRG-like clones. 2) The AtDRG1 promoter will be isolated from a genomic clone and fused to the GUS reporter gene to determine patterns of promoter expression during development. 3) Transgenic plants that overexpress sense, antisense and dominant-negative DRG constructs will be analyzed for their effects on plant growth and development. Other plant systems are being used to probe cellular and biochemical aspects of DRG function and expression. Knowledge gained through these studies should be relevant to DRG function in all organisms.